An operating temperature of a gas turbine has been increasing year by year in order to increase the efficiency thereof. To cope with such a high operating temperature, a thermal barrier coating (which is referred to TBC hereinafter) made of ceramic has been conventionally applied to gas turbine components. As the thermal barrier coating, an MCrAlY alloy layer having high oxidation resistance and a zirconia (ZrO2) based ceramic layer having low thermal conduction are generally formed on a substrate made of a nickel (Ni) based or a cobalt (Co) based alloy (see Example 1 in JP-A-62-211387, for instance). Regarding the “MCrAlY” alloy, M represents at least one element selected from a group consisting of iron (Fe), nickel and cobalt, Cr represents chromium, Al represents aluminum, and Y represents yttrium.